SOLID & Design Patterns Interview Question #50

How do SOLID principles and design patterns work together?

Structural, Creational & Behavioral Patterns Mid-Level Intermediate

Quick Interview Answer

SOLID principles describe desirable dependency and responsibility characteristics, while design patterns provide reusable structures for recurring design problems. Patterns such as Strategy, Decorator, Factory, and Adapter can help implement SOLID principles when the problem genuinely requires them.

Detailed Explanation

Patterns should not be added merely to demonstrate architecture. A strong design uses the simplest structure that keeps responsibilities clear, dependencies controlled, behavior testable, and future changes reasonably localized.

Code Example

// DIP + Strategy example
public interface ITaxStrategy
{
    decimal Calculate(decimal amount);
}

public class CheckoutService
{
    private readonly ITaxStrategy _tax;

    public CheckoutService(ITaxStrategy tax)
        => _tax = tax;
}